Particle beam devices are a class of electrical devices that emit a particle beam for various purposes. In the case of electron beams, the particular beam device may be an electron gun/emitter. While the disadvantages of existing electron guns are described below, it should be noted that these disadvantages equally apply to other types of particular beam devices (e.g. positively or negatively charged ion beams).
In the case of electron guns, these devices typically operate to produce a controlled electron beam, namely by accelerating and/or focusing (condensing) the electron beam. In some basic implementations, electron guns are configured with permanent magnets to control the electron beam. The magnets are permanently situated within the electron gun housing to shape a magnetic field which controls the electron beam.
To the author's knowledge all electron guns have a dedicated extractor electrode that controls the electric field in the emitter region. FIG. 1 shows one example of a configuration of a permanent-magnet electron gun having an extractor for control of emission current, in accordance with the prior art. As shown, FIG. 1 includes an extractor 107A, 107B situated near the electron emitter 102. The extractor 107A, 107B accelerates the electron beam 106 emitted by the electron emitter 102 at an opening thereof and then directs the electron beam 106 through a smaller opening towards the permanent magnets 104A, 104B. This permanent magnet element 104A, 104B provides a magnetic lens that condenses the electron beam 106. A more detailed description of this type of permanent-magnet electron gun is described in U.S. Pat. No. 8,513,619 to Nasser-Ghodsi et al., filed May 10, 2012 and entitled “Non-planar extractor structure for electron source.” Most ideally the extractor controls the emission without impacting the condensing caused by the permanent magnet lens. However, in an actual implementation of the prior art (such as U.S. Pat. No. 8,513,619 to Nasser-Ghodsi et al.) the extractor impacts both emission and condensing of the electron gun, making its operation difficult. Furthermore, the extractor shown therein has a deep well that can be difficult to fabricate, presents a trapped volume and poor local vacuum at the emitter location.
One solution that helps address the shortcoming in control of condensing from permanent-magnet electron guns is the deployment of a magnetic coil instead of permanent magnets. The coil enables a tunable magnetic field, but unfortunately it requires electrical power to generate the magnetic field. This in turn requires the electron gun housing to be larger than the permanent-magnet counterparts, such as that described above, in order to account for the coil and power supply connection.
There is thus a need for addressing these and/or other issues associated with the prior art permanent-magnet based charged particle gun devices.